This grant is directed towards extending our understanding of the structure and function of interphase chromatin. We have proposed that sequence surveillance of the entire chromosomal material occurs as a consequence of a sequential histone acetylation and chromatin unwinding. We wish to check if such modifications occur in genes which are transcriptionally active and distributed over many chromosomes. Further we wish to develop an in vitro deacetylation system in order to further extend our understanding of the nature of the changes in the deacetylase in a series of HTC variant cell lines which are capable of growth in the presence of sodium butyrate and which show an altered deacetylase phenotype. We are particularly interested in testing the relationship between the presence of an altered deacetylase and the ability to overcome the butyrate mediated inhibition of dexamethasone induction of tyrosine aminotransferase. We also wish to develop further a system which we have developed for the fractionation of transcriptionally active chromatin. We hope to use this separation system to analyze nucleosome organization and distribution during the active transcription process. Finally, we wish to test various hypotheses for the movement of histones from the nucleosome proximal to the approaching RNA polymerase during transcription. We plan to approach this initially using model systems in vitro and hopefully later to extend this to an in vivo analysis.